Filling Azek nail holes

Anybody have any suggestion to fill nail holes on Azek? I've heard the Azek 2-part filler doesn't work. I've tried a couple of glazing compounds but they attract dirt/mold and look worse than the holes. I've thought about silicone calk?

I can't comment on weather it discolors as of yet, since it's only been up for about a month or so.

you could also look into the FastenMaster concealed screw system for pvc trim. I tried it out on my front door trim with mixed results. The plugs provided don't always sit flush and sometimes sink in too deep. so there was still something to be filled with spackle or caulk, but not a deep hole. This was only an issue at the front door since the trim was so visible. I think it'd fine on a window without any filler since it wouldn't be as visible.